Alarm circuit supervisory means

ABSTRACT

There is disclosed in an alarm system, a supervisory signal monitoring circuit for providing an indication of a disruption in the system and comprising supervisory conductor means for normally carrying a supervisory current, termination circuit means coupled to the supervisory conductor means, and a trouble indicating circuit coupled to the supervisory conductor means. The trouble indicating circuit includes an oscillator circuit having first circuit means for developing an oscillating signal and second circuit means for applying the oscillating signal to the supervisory conductor means to thereby cause a supervisory current to flow through the conductor means, resistive means coupled to the supervisory conductor means for developing a control signal in response to the flow of the supervisory current, trouble indicating means, and signal responsive circuit means coupled to the control signal developing means in response to the absence of the control signal to thereby provide an indication of a disruption in the supervisory conductor means.

[i nited States Patent [72] ln enlor Robert B. McLeod CllntomMass. 2- 1Appl No. 877,107 [22] Filed Nov. 17, 1969 [45} Patented Aug. I0. 1971{73] Assignee Gulf & Western Systems Company New York, NY.

{545 ALARM CIRCUIT SUPERVISORY MEANS 20 Claims, 2 Drawing Figs.

' s2 u.s.ci. 340/409, 340/227, 340/276 51 Int. Cl G08b 29/00 [50] Field0! Search 340/256,

[56] References Cited UNITED STATES PATENTS 3,500,394 3/]970 Egesdal l.340/409 REMOTE MONITORING CIRCUIT- MC Primary Examiner Donald J. YuskoAttorney-Meyer, Tilberry and Body ABSTRACT: There is disclosed in analarm system, a supervisory signal monitoring circuit for providing anindication of a disruption in thefsystem and comprising supervisoryconductor means for normally carrying a supervisory currenL terminationcircuit means coupled to the supervisory conductor means, and a troubleindicating circuit coupled to the supervisory conductor means. Thetrouble indicating circuit includes an oscillator circuit having firstcircuit means for developing an oscillating signal and second circuitmeans for applying the oscillating signal to the supervisory conductormeans to thereby cause a supervisory current to flow through theconductor means, resistive means coupled to the supervisory conductormeans for developing a control signal in response to the flow of thesupervisory current, trouble in' dicating means, and signal responsivecircuit means coupled to the control signal developing means in responseto the absence of the control signal to thereby provide an indication ofa disruption in the supervisory conductor means RC-C i l 5 l v-2 M- A 1RESONANT ll 5 I L-l yNETWORK-RN 1 l I 3 tine I I l i ALARM CIRCUIT-AC IALARM ALARM l f t i 2 I I2 BELL BE L I TB S 6 I A-I l A-Zl l6 5 t lTROUBLE 4 BUZZER -56 v I fl L WW I t I8 20 I 22 l 36 L 5 I l 48 l 26 I.134 w I T 2 k 28 A :32 40 1 I 1 l l (L J L 1 SUPERVISORY (POWERTOSCILLATOR sensms CIRCUIT-5 SUPPLY-PS CIRCUIT-0 NETWORK -SN ALARMCIRCUIT SUPERVISORY MEANS BACKGROUND OF THE INVENTION This applicationpertains to the art of electrical supervisory and monitoring circuits.and, more particularly, to circuits for monitoring the continuity of anelectrical circuit and providingan indication of a disruption therein.

The invention is particularly applicable to alarm systems, such asindustrial fire alarm systems, and will be described with particularreference thereto, although it will be .appreciated that the inventionhas broader applications, such as, for example, in industrial electricallighting systems, electronic control systems, etcetera. I

The need for supervision of certain electrical circuits, such as alarmcircuits, in order to provide an indication of a disruption in thecontinuity of the circuit, has long been recognized. Various techniqueshave heretofore been employed to provide the necessary supervision ofalarm circuits. One such technique includes a circuit configuration inwhich a plurality of fire alarm indication means, such as alarm bells,are connected in series with a voltage supply source. Alsoconnected inseries with the series-connected alarm bells is an electromechanicalrelay, which, upon an interruption of the electrical continuity of theseries circuit, is actuated to thereby energize a trouble indicatingbuzzer indicative of the circuit interruption. Generally, the relay ismaintained in an energized condition by a small supervisory currentflowing through he series circuit until such time as an interruptionoccurs in the circuit. in a series-connected circuit such as thatdescribed, the-addition or removal of one or more alarm devices requiresthat compensating adjustments be made elsewhere in the circuit in orderto maintain the requisite value of supervisory current. In addition, ina series-connected system of this type, the failure of even a singlealarm device to operate when the system is actuated, causes the entiresystem to fail to operate.

Another technique heretofore employed to provide supervision of an alarmsystem is a circuit comprised of a plurality of alarm indicating meansconnected in parallel across a directcurrent voltage supply source.Switch means are employed in the alarm system to change the effectivepolarity of the direct current voltagesource, which in turn causes thedirection of current flowing within the alarm circuit to change from anormal condition to an alarm condition. This system also includes aplurality of polarity sensing means, such as diodes, con nected inseries with each. of the-alarm indicating means so that a current isallowed to flow through the alarm indicating means when. the switchmeans is in the alarm position, and prevented from. flowing through. thealarm indicating means when the switch means is in normal position. Inaddition, a relay is connectedin the parallel circuit with the switchmeans in a manner so that the relay is energized whenever continuity ismaintained .in the: parallel circuit. The US. Pat. No. 3,309,685, to D.Manning entitled "Supervisory Circuit," and issued. on-Mar. 14, I967,discloses sucha supervisory circuit. The main disadvantage of such asupervisory circuit is that a relatively large power supply must beemployed to convert. the altemating-current line voltage to adirect-current voltage for energizing the supervisory circuit. inaddition, only direct-current type alarm indicating means may beutilized in such a system.

SUMMARY OF THE INVENTION The present invention discloses a new andimproved supervisory circuit which overcomes all of the above referredto problems, and others, and'provides a supervisory circuit which issimple in construction and dependable in operation.

in accordance with one aspect of the present invention, there isprovidedan alarm system comprising a remote station monitoring circuitincluding actuatable means, for upon actuation, transmitting an alarmsignalindicative of an alarm condition at the remote station; alarmcircuit means electrically connected to the remote station monitoringcircuit. The alarm circuit includes alarm indicating means and firstcircuit means for energizing the alarm indicating means in response toan alarm signal, resonant circuit means coupled to said first circuitmeans for normally carrying a supervisory current, and a supervisorycircuit coupled to the first circuit means. In addition, the supervisorycircuit includes an oscillator circuit having second circuit means fordeveloping an oscillating signal to the first circuit means to therebycause the supervisory current to flow through the first circuit means,resistive means coupled tothe first circuit means for developing a control signal in response to the absence of the flow of a supervisorycurrent resulting from a disruption in the electrical connection betweenthe alarm circuit means and the monitoring circuit, trouble indicatingmeans, and signal responsive circuit means coupled to the control signaldeveloping means for there is provided a supervisory signal monitoringsystem for providing an indication of a disruption in the system andcomprising supervisory conductor means for normally carrying asupervisory current, termination'circuit means coupled to thesupervisory conductor means, and a trouble indicating circuit coupled tothe supervisory conductor means. The troubleindicating circuit includesan oscillator circuit having first circuit means for developing anoscillating signal and second circuit means for applying the oscillatingsignal to the supervisory conductor means to thereby cause a supervisorycurrent to flowthrough the conductor means, resistive means couple tothe supervisory conductor means for developing a control signal inresponse to the flow of the supervisory current, trouble indicatingmeans, and signal responsive circuit means coupled to the control signaldeveloping means for energizing the trouble indicating means in responseto the absence of the control signal to thereby provide an indication ofa disruption in the supervisory conductor means.

In accordancewith amore limited aspect of the present invention, thetermination circuit means is comprised of a capacitive and/oraninductive circuit element.

in accordance with a still more limited aspect of the present invention,the termination circuit means is comprised of a capacitive elementconnected in series with an inductive element wherein the seriesconnectedelements are connected in parallel with the alarm indicatingmeans.

In accordance with another aspect of the present invention, thetermination circuit means is a resonant circuit means and includes acapacitive and an inductive element.

The principle object of the present invention is'to provide asupervisory circuit which is responsive to the absence of a supervisorycurrent for providing an indication of a disruption in an electricalcircuit.

Another object of the present invention is to provide a supervisorycircuit which is responsive to a supervisory current for, upon theabsence of the supervisory current, energizing a trouble indicatingmeans, such as a trouble buzzer or bell.

A further object of the present invention is to provide a supervisorysignal monitoring circuit which eliminates current compensatingresistors in the alarm circuit to thereby eliminate the adjustment ofthese compensating resistors, and

the readjustment of these resistors whenever alarm indicating BRIEFDESCRIPTION OF THE DRAWINGS These and other objects and advantages ofthe invention will become apparent from the following description of thepreferred embodiments of the invention as read in connection with theaccompanying drawings in which:

FIG. 1 is a schematic circuit diagram illustrating the preferredembodiment of the invention in conjunction with the alarm system; and,

FIG. 2 is a schematic circuit diagram of a second aspect of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingswherein the showings are for purposes of illustrating a preferredembodiment of the invention and not for purposes of limiting same, FIG.1 illustrates the supervisory signal monitoring circuit employed inconjunction with an alarm system, and generally comprises analternating-current voltage supply source Vl connected to an alarmcircuit AC and a supervisory monitoring circuit S. Supervisorymonitoring circuit S is generally comprised of a power supply circuitPS, an oscillator circuit 0, and sensing network SN.

More particularly, one of the terminals of voltage supply source V-l,which preferably takes the form of an alternatingcurrent line source, isconnected through a normally open switch 8-1 to one of the terminals 1of one of the sets of contacts 10 of an alarm relay RC. The otherterminal of voltage supply source V-l is connected directly to one ofthe terminals 2 of the other set of contacts 12 of alarm relay RC. Thetwo sets of relay contacts l0, 12 of alarm relay RC generally take theconfiguration of a double-pole, double-throw switch which is actuated bya relay coil RC-C. Relay coil RC-C of alarm relay RC is connected inseries with a normally open alarm actuator A and a voltage supply sourceV-2, which preferably takes the form of a direct-current voltage source.

Relay contacts 10 and 12 respectively include a pair of movable contactsand 6, which are respectively connected to a pair of lines L-l and L-2of alarm circuit AC. Connected in parallel, and across lines Lr-I andL-2 of the alarm circuit AC, are a pair of alarm bells A-1 and A-2, anda resonant network RN. As is readily apparent, alarm bells A-1 and A-2may take the form of various alarm indicating devices, such as bells,lamps, buzzers, etc. In addition, while only two alarm bells A-1 and A-2are illustrated in the preferred embodiment, it is contemplated that anynumber of such devices could be connected across lines L-l and D4 ofalarm circuit AC. Preferably, the impedance of each alarm device isrelatively high in comparison to the impedance exhibited by resonantnetwork RN as will be discussed hereinafter. Resonant network RN iscomprised of an inductive element 14 connected in parallel with acapacitive element 16 across lines L-l and L-2 of alarm circuit AC. Inthe preferred embodiment of the present invention, inductor l4 andcapacitor 16 are of the fixed type; however, it is-contemplated thateither one or both of these elements could be made variable in order tovary the resonant frequency exhibited by resonant network RN.

Terminals I and 2 of relay contacts and 12 are respectively connected toa common ground connection and to the anode of a diode 18 in powersupply circuit PS. The cathode of diode 18 is connected through a pairof series-connected resistors 20 and 22 to an output terminal 24 ofpower supply circuit PS. The junction point between resistors 20 and 22is con nected through a capacitor 26 to ground, and the output ter minal24 of power supply circuit PS is connected through a Zener diode 28,poled as shown in FIG. 1, to ground.

The output terminal 24 of power supply circuit PS is connected through apair of series-connected resistors 30 and 32 in oscillator circuit 0 toground. The junction point between series-connected resistors 30 and 32is connected to the base of a PNP transistor 34 having its emitterconnected through a resistor 36 to the output terminal 24 of powersupply circuit PS. The emitter of transistor 34 is also connectedthrough a capacitor 38 to the output terminal 24 of power supply circuitPS, and the collector of this transistor is connected through a resistor40 to ground. Also, the collector of transistor 34 is connected throughthree series connected capacitors 32. 44 and 46 to the base of thistransistor. The junction point between capacitors 42 and 44 is connectedthrough a seriesconnected variable resistor 48 and fixed resistor 50 tooutput terminal 24 of power supply circuit PS. Similarly, the junctionpoint between capacitors 44 and 46 is connected through aseries-connected variable resistor 52 and fixed resistor 54 to outputterminal 24 of power supply circuit PS. Variable resistors 48 and 52 arepreferably connected in common so that the impedances of these resistors48 and 52 may be varied in common.

The collector of transistor 34 is also connected directly to the base ofan NPN transistor 55 having its collector con nected directly to outputtenninal 24 of power supply circuit PS, and its emitter connectedthrough a resistor 57 to ground. The emitter of transistor 55 is alsoconnected through a capacitor 56 to a third terminal of relay contact 10of alarm relay RC. A third contact 4 of relay contact 12 of alann relayRC is connected through a variable resistor 60 to ground, and is alsoconnected through a series-connected resistor 62 and capacitor 64 to thebase of an NPN transistor 56. Also, the base of transistor 66 isconnected through a resistor 68 to ground, and the emitter of thistransistor is connected through a pair of series-connected diodes 70 and72, poled as shown in FIG. 1, to ground. Connected to the collector oftransistor 66 is one terminal of a relay coil TR-C of trouble relay TR.The other terminal of coil TR-C is connected directly to output terminal24 of power supply circuit PS. Also, connected to the collector oftransistor 66 is one terminal of a capacitor 74 having the otherterminal thereof connected to output terminal24 of power supply circuitPS. Trouble relay TR also includes a pair of normally closed relaycontacts TR-l which are connected in series with a trouble buzzer TB anda direct-current voltage supply source V-3.

OPERATION OF PREFERRED EMBODIMENT Upon closure of normally open switchS1, an alternating current signal is applied to terminals 1 and 2 ofrelay contacts 10 and 12 of alarm relay RC. Also, the alternatingcurrent signal is applied through power supply circuit PS to provide aconstant direct-current output signal at output terminal 24 of powersupply circuit PS. Zener diode 28 of power supply circuit PS serves as avoltage regulator for maintaining a relative ly constant voltagedirect-current signal at output terminal 24. This direct-current outputsignal is applied to oscillator circuit 0 which is generally comprisedof an amplifier circuit including transistor 34 and its associatedcircuitry, and a phase shift network including capacitors 42, 44, and46, and resistors 48, 50, 52, and 54. Oscillator circuit 0 operates in amanner similar toEonventional phase shift oscillators in that theamplifier circuit provides a phase shift of and the phase shift networkprovides an additional phase shift of 180", which is in turn fed back tothe input circuit of the amplifier circuit, i.e., the base terminal oftransistor 34. The frequency of oscillation of oscillator circuit 0 maybe readily varied by altering the impedance of potentiometers 48 and 52.The output signal of the phase shift oscillator is applied through anamplifier including transistor 55 and resistor 57, and a blockingcapacitor 56 to terminal 3 of alarm relay RC.

The oscillating frequency signal applied to terminal 3 of alarm relay RCis in turn applied through resonant network RN and potentiometer 60 toground. In addition, alarm indicating devices, such as alarm bells A-land A-2, are coupled in parallel with each other and with resonantnetwork RN. The frequency of oscillation is chosen so that the impedanceexhibited by alarm bells A-1 and A-2 is relatively high in comparison tothe impedance of variable resistor 60,

andthe value of impedance of variable resistor 60 is chosen so tliattheimpedance of resonant network RN is relatively low in comparison to theimpedance exhibited by variable resistor ll-Thus, when supervisory linesL4 and L-2 are in tact, substantially all ofthe output voltage developedby oscillator circuitt) is applied across sensingpotentiometer 60thereby causing transistor 6610 become forward biased. With transistor66 in a forward .biasedcondition, trouble relay TR will become energizedthereby preventing energization of trouble buzzer TB.

Whenever either of the supervisory lines L-I or I..-2 is disrupted, thecurrent flowing through resonant network RN is also disruptednherebycausing substantially all of the voltage developedby oscillator circuit0 to be applied across the alarm bells A-l and A-2 remaining in thecircuit. With substantially all of the voltagedcveloped by oscillatorcircuit 0 appliedacross alarm bells A-1 and A4, the voltage appliedacross sensing potentiometer 60 decreases to substantially zero volts,thereby reverse biasing; transistor 66. Upon reverse biasing transistor66, trouble relay TR becomes deenergized thereby energizing troublebuzzer TB. Similarly. if the disruption of lines L-! and b-Z occursbetween alarm relay RC and alarm bell A-l, the current flowing throughsensing potentiometer 60 is removed, thereby causing the voltagedeveloped across sensing potentiometer to decrease to zero volts. Again,transistor becomes reverse biases thereby causing trouble buzzer TB tobecome energized.v

Upon closure of normally open alarm actuator A, alarm relay RC becomesenergized thereby causing relay armatures 5 and.6 to respectively movefrom relay contacts 3 and 4 to I relay contactslandl With tberelayarmatures in this condition, the alternating-current voltage'signaldeveloped by voltage source-VJ is applied-directly across alarm bellsA-1 and A-2. Thus, alarm actuator A serves the function-of, uponclosure, energizing alarm bells A-1 and A-2. In addition, upon-adisruption in the supervisory lines L-l and [4-2, trouble buzzer. ZTB-isenergized'thereby providing anindication of the disruption.

oasckrmouor THE-SECQND-EMBODIMENT Reference .is-now made to FIG. 2 whichgenerally illustrates a second-embodiment of the present invention whichis quite nectcdthrough impair.ofseriessconnectedresistors 82 and 84-" toground. The junctionpointb'etween resistors 82 and 84 is connectedto-the baselof a PNP-transistor 86 having its emitterconnected-'through-a resistor 87 to terminal 24 of power supplycircuivRS: The emitter of transistor-86 is also connected-throughaucapscitor 88 to terminal 24 of power supply circuit- FS, nandthecollector of this transistor is connected through a resistor 90 mground. Also, the collector of transistor connected through threeseries-connected capacitors; 94' and 96=to thev base of this transistor.The

junction 'point between capacitors and=94 is connected through a:resistor 98 to terminal 24 of power supply circuit PS,andz-the-junctionpoint betweencapacitors-M and 96 is connectedithroughaaresistor: 100' to terminal 24 of power supplyPS; In addition-,-;thecollector of transistor 86 is connected through .aseriesmonnectedresistor 102 and capacitor ltwt'o the baseofanNPNtransistor 106.

The base-oi. transistor-106- is connected through a resistor l08=toterminal-24' of-power-supply circuit PS 'andthrough a.

resistor 110 110 ground. Connected between the collector of transistorlo6 and=terminal 24 of power supply circuit PS is a 6 resistor 112, andconnected betweon this collector and ground is a capacitor 114. Theemitter-oftransistor 106i: connected through a resistor 116 to ground-andis also connected to blocking capacitor 56.

Sensing network SN-l is somewhat similar to the sensing network SN asillustrated in FIG. 1, however, potentiometer is replaced with a fixedresistive element I18. resistive element 62 is deleted, a resistorl20=is connected between the base of transistor 66 and terminal=24 ofpowersupply circuit PS, and diodes element 122.

OPERATION OF THE SECOND EMBODIMENT The supervisory circuit asillustrated in FIG. 2 operates in a manner substantially similar to thecircuit illustrated in FIG. 1 however, a buffer stage includingtransistor l-06-has b'e'enincorporated between the output circuit of theoscillator circuit and the alarm circuit AC-l. In addition, a singlecapacitive element has been employed to replace the tuned-resonantnetwork RN with the net effect that the frequency ofoscillation andvalues of circuit components are less critical. As with the supervisorycircuit illustratedin FIG. 1, upon actuation-of" the alarm actuator A,alann bells A-1 and A2 are energized thereby providing an alarmindication. Similarly, upon disruption of either of the supervisorylines L-l or L-the voltage developed across sensing resistor 118decreasesto substantially zero volts, thereby reverse biasing transistor6 which, in

and 72 are replaced with a single resistive turn, causes trouble buzzerTB to become energized:' In ac-- TABLE I Element No. Component Value erType V-] I 15 volts 14 I0 microhenry 16 0.047 mlcrofarud ll IN3255 20 lkilo ohm 22 7.5 kilo ohms 26 40 microfarad 28 24 volt: 30 L2 kilo ohms32 22 kilo ohms 34 ZNSOBA 36 220 ohms 38 22 microl'lrad 40 l .2 kiloohms 42, 44, 46 0.22 microfarld I, 52 I00 ohms 50, 54 720 ohm: 57 3.2kilo ohms 62 S l kilo ohms 64 0.01 'microl'and 66 2N3? 8 2.2 kilo ohms22 microfand TR IBM760S Frequency of oscillation 2.5 kilohertz Inaccordance with the second embodiment of the present invention, thevalues and types of various components illustrated in FIG. 2 are foundin TABLE".

TABLE II Element No. Component Value or Type 80 l microflrad 82 L8 kiloohms B4 22 kilo-ohms 86 ZNSOBA 81 220 kilo Ollml 88 47 microlarld 90 L2kilo ohms nrnPOnCfll Value or [we I lr-mem No 91.94 96 0,01 microfarad9!. I 820 ohms 102 4.7 kilo ohm! IN 0.22 microflrad I 2N34l7 I00 I 2kilo ohm: "0 3.5 kilo ohm: H1 270 ohms IH 25 microfarad 1| I50 ohm:

150 ohm! l1. 6! kilo ohnu In 33 ohms Frequency of oscillation kilocycles Although the invention has been shown in connection with apreferred embodiment, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

Having thus described my invention, I claim:

1. An alarm system comprising:

a remote station monitoring circuit including actuatable means, for uponactuation, transmitting an alarm signal indicative of an alarm conditionat the remote station;

lilarm circuit means electrically connected to said remote stationmonitoring circuit; said alarm circuit means including:

alarm indicating means and first circuit means for energiz ing saidalarm indicating means in response to a said alarm signal;

resonant circuit means coupled to said first circuit means for normallycarrying a supervisory current; and,

a supervisory circuit coupled to said first circuit means and including;

an oscillator circuit having second circuit means for developing anoscillating signal and third circuit means for applying a saidoscillating signal to said first circuit means to thereby cause a saidsupervisory current to flow through said first circuit means and saidresonant circuit means;

means coupled to said first circuit means for developing a controlsignal in response to the absence of the flow of a said supervisorycurrent resulting from a disruption in the electrical connection betweenthe alarm circuit means and the monitoring circuit;

trouble indicating means; and,

signal responsive circuit means coupled to said control signaldeveloping means for energizing said trouble indicating means inresponse to the receipt of a said control signal to thereby provide anindication of a disruption in the electrical connection between saidalarm circuit means and the monitoring circuit.

2 An alarm system as set forth in claim 1 wherein said resonant circuitmeans is comprised of a capacitive element.

3; An alarm system as set forth in claim 2 wherein said resonant circuitmeans also includes an inductive element.

4; An alarm system as set forth in claim 3 wherein said capacitive andinductive elements are connected together in a series electricalconfiguration.

5, An alarm system as set forth in claim 4 wherein said seriesconnectedcapacitive and inductive elements are connected in parallel with saidalarm indicating means.

6. An alarm system as set forth in claim 5 wherein said first circuitmeans includes a pair of conductors being connected across saidseries-connected capacitive and inductive elements.

7, An alarm system as set forth in claim 6 wherein said con- :rol signaldeveloping means is a resistive means connected to JT| of said pair ofconductors for developing a signal of a )redetermined value with respectto ground potential in "espouse to the flow of a said supervisorycurrent through said irst circuit means and a signal having a valuesubstantially :qual to ground potential with respect to ground potentialin he absence of the flow of a said supervisory current.

8. ln an alarm system a supervisory signal monitoring system comprising:

alarm circuit means including;

alarm indicating means and first circuit means for energizing said alarmindicating means in response to the receipt of an alarm signal; and,

resonant circuit means coupled to said first circuit means for normallycarrying a supervisory current; and,

a supervisory circuit including;

an oscillator circuit having a second circuit means for developing anoscillator signal and a third circuit means electrically connecting saidsecond circuit means to said resonant circuit means;

means coupled to said third circuit means for developing a controlsignal in response to the absence of the flow of a said supervisorycurrent resulting from a disruption in the electrical connection betweenthe third circuit means and the resonant circuit means;

trouble indicating means; and,

signal responsive circuit means coupled to said control signaldeveloping means for energizing said trouble indicating means inresponse to a said control signal developed by said signal developingmeans to thereby provide an indication of a disruption in the electricalcon nection between the third circuit means and the resonant circuitmeans.

9. In an alarm system as defined in claim 8 wherein said resonantcircuit means is comprised of a capacitive element.

10. In an alarm system as defined in claim 9 wherein said resonantcircuit means also includes an inductive element,

11. In an alarm system as defined in claim 10 wherein said capacitiveelement is electrically connected in series with said inductive element.

12. in an alarm system as defined in claim 11 wherein saidseries-connected capacitive and inductive elements are connected inparallel with said alarm indicating means 13. An alarm systemcomprising:

a remote station monitoring circuit including actuatahle means, for uponactuation, transmitting an alarm signal indicative of an alarm conditionat the emote station;

alarm circuit means electrically connected to said remote stationmonitoring circuit; said alarm circuit means meluding;

alarm indicating means and first circuit means for energizing said alarmindicating means in response to a said alarm signal; and,

capacitive means coupled to said first circuit means for normallycarrying a supervisory current; and,

a supervisory circuit coupled to said first circuit means and including;

an oscillator circuit having second circuit means for developing anoscillating signal and third circuit means for applying a saidoscillating signal to said first circuit means to thereby cause a saidsupervisory current to flow through said first circuit means and saidcapacitive means;

means coupled to said first circuit means for developing a controlsignal in response to the absence of the flow of a said supervisorycurrent resulting from a disruption in the said electrical connectionbetween the alarm circuit means and the monitoring circuit;

trouble indicating means; and,

signal responsive circuit means coupled to said control signaldeveloping means for energizing said trouble indicating means inresponse to the receipt of a said control signal from said signaldeveloping means to thereby pro vide an indication of a disruption inthe electrical connection between said alarm circuit means and themonitoring circuit.

14. A supervisory signal monitoring system for providing an indicationof a disruption in said system and comprising:

supervisory conductor means for normally carrying a supervisory current;

termination circuit means coupled to said supervisory con ductor means;

a trouble indicating circuit coupled to said supervisory conductor meansand including;

an oscillator circuit having first circuit means for developing anoscillating signal and second circuit means for applying saidoscillating signal to said supervisory conductor means to thereby causea said supervisory current to flow through said supervisory conductormeans;

means coupled to said supervisory conductor means for developing acontrol signal in response to the flow of a said supervisory currentthrough said supervisory conductor means;

trouble indicating means;

signal responsive circuit means coupled to said control signaldeveloping means for energizing said trouble indicating means inresponse to the absence of a said control signal to thereby provide anindication of a disruption in the supervisory conductor means.

15. A supervisory signal monitoring system as defined in claim 14wherein said termination means is comprised of a capacitive element.

16. A supervisory signal monitoring system as defined in claim 14wherein said termination means is comprised of an inductive element.

17. A supervisory signal monitoring system as defined in claim 14wherein said termination means is a resonant network including acapacitive element and an inductive element.

18. A supervisory signal monitoring system as defined in claim 17wherein said capacitive and inductive elements are electricallyconnected in series to said supervisory conductor means.

19. A supervisory signal monitoring system as defined in claim 14wherein said supervisory conductor means is comprised of a pair ofconductors and said termination circuit means is comprised of acapacitive element connected across said pair of conductors.

20. A supervisory signal monitoring system as defined in claim 19wherein said control signal developing means is a resistive elementcoupled to one of said pair of conductors and said signal responsivecircuit means includes;

electronic control means having an input circuit means and an outputcircuit means, and a first and a second condition; said input circuitmeans of said electronic control means being coupled to said resistive elernentso that upon the absence of a said control signal said electroniccontrol means is actuated from said first condition to said secondcondition; and, said output circuit means of said electronic controlmeans being coupled to said trouble indicating' means to therebyenergize said trouble indicating means wherever said electronic controlmeans is actuated from said first condition to said second condition.

1. An alarm system comprising: a remote station monitoring circuitincluding actuatable means, for upon actuation, transmitting an alarmsignal indicative of an alarm condition at the remote station; alarmcircuit means electrically connected to said remote station monitoringcircuit; said alarm circuit means including: alarm indicating means andfirst circuit means for energizing said alarm indicating means inresponse to a said alarm signal; resonant circuit means coupled to saidfirst circuit means for normally carrying a supervisory current; and, asupervisory circuit coupled to said first circuit means and including;an oscillator circuit having second circuit means for developing anoscillating signal and third circuit means for applying a saidoscillating signal to said first circuit means to thereby cause a saidsupervisory current to flow through said first circuit means and saidresonant circuit means; means coupled to said first circuit means fordeveloping a control signal in response to the absence of the flow of asaid supervisory current resulting from a disruption in the electricalconnection between the alarm circuit means and the monitoring circuit;trouble indicating means; and, signal responsive circuit means coupledto said control signal developing means for energizing said troubleindicating means in response to the receipt of a said control signal tothereby provide an indication of a disruption in the electricalconnection between said alarm circuit means and the monitoring circuit.2. An alarm system as set forth in claim 1 wherein said resonant circuitmeans is comprised of a capacitive element.
 3. An alarm system as setforth in claim 2 wHerein said resonant circuit means also includes aninductive element.
 4. An alarm system as set forth in claim 3 whereinsaid capacitive and inductive elements are connected together in aseries electrical configuration.
 5. An alarm system as set forth inclaim 4 wherein said series-connected capacitive and inductive elementsare connected in parallel with said alarm indicating means.
 6. An alarmsystem as set forth in claim 5 wherein said first circuit means includesa pair of conductors being connected across said series-connectedcapacitive and inductive elements.
 7. An alarm system as set forth inclaim 6 wherein said control signal developing means is a resistivemeans connected to one of said pair of conductors for developing asignal of a predetermined value with respect to ground potential inresponse to the flow of a said supervisory current through said firstcircuit means and a signal having a value substantially equal to groundpotential with respect to ground potential in the absence of the flow ofa said supervisory current.
 8. In an alarm system a supervisory signalmonitoring system comprising: alarm circuit means including; alarmindicating means and first circuit means for energizing said alarmindicating means in response to the receipt of an alarm signal; and,resonant circuit means coupled to said first circuit means for normallycarrying a supervisory current; and, a supervisory circuit including; anoscillator circuit having a second circuit means for developing anoscillator signal and a third circuit means electrically connecting saidsecond circuit means to said resonant circuit means; means coupled tosaid third circuit means for developing a control signal in response tothe absence of the flow of a said supervisory current resulting from adisruption in the electrical connection between the third circuit meansand the resonant circuit means; trouble indicating means; and, signalresponsive circuit means coupled to said control signal developing meansfor energizing said trouble indicating means in response to a saidcontrol signal developed by said signal developing means to therebyprovide an indication of a disruption in the electrical connectionbetween the third circuit means and the resonant circuit means.
 9. In analarm system as defined in claim 8 wherein said resonant circuit meansis comprised of a capacitive element.
 10. In an alarm system as definedin claim 9 wherein said resonant circuit means also includes aninductive element.
 11. In an alarm system as defined in claim 10 whereinsaid capacitive element is electrically connected in series with saidinductive element.
 12. In an alarm system as defined in claim 11 whereinsaid series-connected capacitive and inductive elements are connected inparallel with said alarm indicating means
 13. An alarm systemcomprising: a remote station monitoring circuit including actuatablemeans, for upon actuation, transmitting an alarm signal indicative of analarm condition at the remote station; alarm circuit means electricallyconnected to said remote station monitoring circuit; said alarm circuitmeans including; alarm indicating means and first circuit means forenergizing said alarm indicating means in response to a said alarmsignal; and, capacitive means coupled to said first circuit means fornormally carrying a supervisory current; and, a supervisory circuitcoupled to said first circuit means and including; an oscillator circuithaving second circuit means for developing an oscillating signal andthird circuit means for applying a said oscillating signal to said firstcircuit means to thereby cause a said supervisory current to flowthrough said first circuit means and said capacitive means; meanscoupled to said first circuit means for developing a control signal inresponse to the absence of the flow of a said supervisory currentresulting from a disruption in the said electrical coNnection betweenthe alarm circuit means and the monitoring circuit; trouble indicatingmeans; and, signal responsive circuit means coupled to said controlsignal developing means for energizing said trouble indicating means inresponse to the receipt of a said control signal from said signaldeveloping means to thereby provide an indication of a disruption in theelectrical connection between said alarm circuit means and themonitoring circuit.
 14. A supervisory signal monitoring system forproviding an indication of a disruption in said system and comprising:supervisory conductor means for normally carrying a supervisory current;termination circuit means coupled to said supervisory conductor means; atrouble indicating circuit coupled to said supervisory conductor meansand including; an oscillator circuit having first circuit means fordeveloping an oscillating signal and second circuit means for applyingsaid oscillating signal to said supervisory conductor means to therebycause a said supervisory current to flow through said supervisoryconductor means; means coupled to said supervisory conductor means fordeveloping a control signal in response to the flow of a saidsupervisory current through said supervisory conductor means; troubleindicating means; signal responsive circuit means coupled to saidcontrol signal developing means for energizing said trouble indicatingmeans in response to the absence of a said control signal to therebyprovide an indication of a disruption in the supervisory conductormeans.
 15. A supervisory signal monitoring system as defined in claim 14wherein said termination means is comprised of a capacitive element. 16.A supervisory signal monitoring system as defined in claim 14 whereinsaid termination means is comprised of an inductive element.
 17. Asupervisory signal monitoring system as defined in claim 14 wherein saidtermination means is a resonant network including a capacitive elementand an inductive element.
 18. A supervisory signal monitoring system asdefined in claim 17 wherein said capacitive and inductive elements areelectrically connected in series to said supervisory conductor means.19. A supervisory signal monitoring system as defined in claim 14wherein said supervisory conductor means is comprised of a pair ofconductors and said termination circuit means is comprised of acapacitive element connected across said pair of conductors.
 20. Asupervisory signal monitoring system as defined in claim 19 wherein saidcontrol signal developing means is a resistive element coupled to one ofsaid pair of conductors, and said signal responsive circuit meansincludes; electronic control means having an input circuit means and anoutput circuit means, and a first and a second condition; said inputcircuit means of said electronic control means being coupled to saidresistive element so that upon the absence of a said control signal saidelectronic control means is actuated from said first condition to saidsecond condition; and, said output circuit means of said electroniccontrol means being coupled to said trouble indicating means to therebyenergize said trouble indicating means wherever said electronic controlmeans is actuated from said first condition to said second condition.